- 第 3 页 -
如果有興趣,可以向這方向去找些資料, 我不太懂..
bit depth =word length
它可以是
1)用來表達音頻檔的精度,
2)也可以是內部計算精度,
3)經過處理的訊號在進入下一處理環節前到底有多少位元
4) cpu, 系統, 計算機總線的精度
The word "bit" is used in a number of contexts in digital audio.
Such as:
* the bit depth of an audio file (i.e. 16bit, 24bit). Each bit is nominally 6dB worth of dynamic range - so 16bits gives you a theoretical 96dB worth of dynamic range while 24bit gives you a whopping 144dB (where as human hearing at the very best has 120dB worth of dynamic range). It's important to realize that even 32bit audio files are output by all modern proaudio Digital to Analog Converter at 24bits. The reason that no DAC ever needs to be designed to actually output at 32bits is that the least significant 24th bit is very well below the noise floor of any environment, and also well below the human ear's ability to detect sound.
* the bit depth of the internal processing math (which can either be floating point or fixed point). What this means is how many digits calculations occur at - bigger bit depths (i.e. more digits to work with) means more precise calculations. SAW uses 64bit fixed point math for its multiplication and division. Most other native PC based DAW apps use 32bit floating point for this. The SAWStudio built in eq, the Anwida and JMS Audioware SAW native plugins, and some of the filter codes used in the Sonoris SAW native plugins use 64bit floating point math.
* the bit depth of the returned figures after a DSP has been performed - i.e. after a signal process is done, how many digits are passed to the next signal process prior to output. In SAW this is at 32bit fixed point using the full DWORD. With most other PC based DAW appps this is a 24bit + 8bit mantissa 32bit IEEE floating point file.
* the bit depth of a computer's buss, cpu, or OS - basically the allowable throughput of data chunks the cpu or buss or OS can pass or process at once. Bigger depths for these functions means more calculations can occur at once - so you get faster speeds - but it does not necessarilly mean that the quality of calculations has changed as this is dependent on the processing algorithm being run. A 32bit OS (such as Windows 2000) can still perform calculations using 64bit math!
****************************************************************************************************************************************
Digital word-length
*Although much literature uses the term 'bit-depth' rather then 'word-length', we chose the term 'word-length' simply because we feel it better describes the mathematical aspect, as well as help to visualize the implication of the technology. It is no more correct or incorrect then using 'bit-depth'; the two terms are synonymous.
Introduction
Word-length (also known as bit-depth) indicates how many digits are used to represent a value in a digital word. For instance, a word-length of 8-bits (8 digits) can only have values from 00000000 to 11111111 (in decimal, 0 to 255). A word-length of 16-bits can have values from 0000000000000000 to 1111111111111111 (0 to 65,536). A digital word doubles in resolution with each bit. For example a 16-bit sample has twice as many possible values (65,536) as a 15-bit word (32,768).
Word-length in digital audio
The word-length of an audio recording determines the amount of noise required to avoid quantization distoration and accurately record and reproduce analog audio signals.
When an analog audio signal is digitally sampled, the voltage on the analog line is sampled several thousand times per second (determined by the sample-rate). Each sample is a 'snap-shot' of the analog waveform at that given moment in time. The sample is a digital word, the value of which is representative of the amplitude of the analog voltage at that moment. With an increase in word-length, the analog voltage can be measured with a finer resolution, making the sample a more accurate description of the value. However, the signal must be dithered to completely avoid quantization distortion.
Common digital audio word-lengths"Redbook", CD audio 16-bit
Professional audio 24-bit
Word-length reduction in digital audio
When digital audio samples are reduced, resolution is inherently lost. Also, if the digital audio is not properly dithered during the reduction, severe distortion will be induced (simply removing the least significant bits without dithering is known as truncation).
[ 本帖最后由 himhui 于 11-1-3 22:03 编辑 ]
bit depth =word length
它可以是
1)用來表達音頻檔的精度,
2)也可以是內部計算精度,
3)經過處理的訊號在進入下一處理環節前到底有多少位元
4) cpu, 系統, 計算機總線的精度
The word "bit" is used in a number of contexts in digital audio.
Such as:
* the bit depth of an audio file (i.e. 16bit, 24bit). Each bit is nominally 6dB worth of dynamic range - so 16bits gives you a theoretical 96dB worth of dynamic range while 24bit gives you a whopping 144dB (where as human hearing at the very best has 120dB worth of dynamic range). It's important to realize that even 32bit audio files are output by all modern proaudio Digital to Analog Converter at 24bits. The reason that no DAC ever needs to be designed to actually output at 32bits is that the least significant 24th bit is very well below the noise floor of any environment, and also well below the human ear's ability to detect sound.
* the bit depth of the internal processing math (which can either be floating point or fixed point). What this means is how many digits calculations occur at - bigger bit depths (i.e. more digits to work with) means more precise calculations. SAW uses 64bit fixed point math for its multiplication and division. Most other native PC based DAW apps use 32bit floating point for this. The SAWStudio built in eq, the Anwida and JMS Audioware SAW native plugins, and some of the filter codes used in the Sonoris SAW native plugins use 64bit floating point math.
* the bit depth of the returned figures after a DSP has been performed - i.e. after a signal process is done, how many digits are passed to the next signal process prior to output. In SAW this is at 32bit fixed point using the full DWORD. With most other PC based DAW appps this is a 24bit + 8bit mantissa 32bit IEEE floating point file.
* the bit depth of a computer's buss, cpu, or OS - basically the allowable throughput of data chunks the cpu or buss or OS can pass or process at once. Bigger depths for these functions means more calculations can occur at once - so you get faster speeds - but it does not necessarilly mean that the quality of calculations has changed as this is dependent on the processing algorithm being run. A 32bit OS (such as Windows 2000) can still perform calculations using 64bit math!
****************************************************************************************************************************************
Digital word-length
*Although much literature uses the term 'bit-depth' rather then 'word-length', we chose the term 'word-length' simply because we feel it better describes the mathematical aspect, as well as help to visualize the implication of the technology. It is no more correct or incorrect then using 'bit-depth'; the two terms are synonymous.
Introduction
Word-length (also known as bit-depth) indicates how many digits are used to represent a value in a digital word. For instance, a word-length of 8-bits (8 digits) can only have values from 00000000 to 11111111 (in decimal, 0 to 255). A word-length of 16-bits can have values from 0000000000000000 to 1111111111111111 (0 to 65,536). A digital word doubles in resolution with each bit. For example a 16-bit sample has twice as many possible values (65,536) as a 15-bit word (32,768).
Word-length in digital audio
The word-length of an audio recording determines the amount of noise required to avoid quantization distoration and accurately record and reproduce analog audio signals.
When an analog audio signal is digitally sampled, the voltage on the analog line is sampled several thousand times per second (determined by the sample-rate). Each sample is a 'snap-shot' of the analog waveform at that given moment in time. The sample is a digital word, the value of which is representative of the amplitude of the analog voltage at that moment. With an increase in word-length, the analog voltage can be measured with a finer resolution, making the sample a more accurate description of the value. However, the signal must be dithered to completely avoid quantization distortion.
Common digital audio word-lengths"Redbook", CD audio 16-bit
Professional audio 24-bit
Word-length reduction in digital audio
When digital audio samples are reduced, resolution is inherently lost. Also, if the digital audio is not properly dithered during the reduction, severe distortion will be induced (simply removing the least significant bits without dithering is known as truncation).
[ 本帖最后由 himhui 于 11-1-3 22:03 编辑 ]
原帖 由 dabeat 于 11-1-4 00:13 发表
這令小弟想起十幾年前, 忽然流行起1-Bit D/A Pulse Flow 的CD Player.
小小弟也只聽聞過, 沒機會正式的去聽....
The original 1-bit scheme high speed pulse flow digital analog converter which neither zero cross distortion nor a glitch noise generates is carried in the D-A-conversion part. A noise shaper is operated on the high oversampling frequency of 384fs, and the re-quatization noise generated in the case of a bit comression is reduced. Thereby, the noise shaper could use it by the sub- and has reduced the influence of an out-of-band noise, an analog low pass filter, etc.
Furthermore, a master clock is operated on the low frequency of 16.93MHz, and the influence of a Jitter is suppressed.
Original compact-disk turntable mechanism which suppresses an unnecessary oscillation of a disk is carried.
Moment of inertia is improving by about 3 times with supporting a disk the whole surface from the bottom.
The direct construction which shortest-ized the signal path is adopted, an analog circuit is connected with the shortest distance, and measures against a noise, such as giving the shielding by the sheet metal made from a copper plating steel plate, are taken.
If the compu-program edit which replaces a music number, and a time of tape are specified so that the residual time of a tapes may become a min only by setting the time of a tapes with remote control,A specification of the time fade edit and time of tape which carry out a fadeout to the time automatically, and will be in a pause status carries the auto special-NetWare-program edit recorded without judging to the how many music it can record, and making the last music break off.
The peek search function, the memory hold facility, the digital ones / analog change-over switch, and the display-deviceoff functionality are carried.
我们假设，将64轨完全不相同的0db电平的信号混合在一起，总电平将会是+18db。为了不让声音过载，我们必须把每一轨的推子拉下来18db。那么我们已经知道了，1bit=6db。那么每一轨的推子拉下来18db将会使所有本来24bit的声音变成了21bit的声音。
是不是可以这样理解，我们16BIT的音乐一个鼓一个BASS，鼓达到0DB, BASS -12DB 那么这个BASS只有14BIT....那这首歌就损失大了。。。BASS音质太烂了，才14BIT。。。。为了不损失BASS我们把BASS拉到0DB。。。。BASS就成了16BIT的BASS了……